function animate(obj,target,callback){

    clearInterval(obj.timer);
    obj.timer = setInterval(function(){

        var step = (target - obj.offsetLeft)/10;
        step = step > 0 ? Math.ceil(step) : Math.floor(step);
        if(obj.offsetLeft == target){
            clearInterval(obj.timer);
            // if(callback){
            //     callback();
            // }

            callback && callback();//短路思想
        }
        obj.style.left = obj.offsetLeft + step + 'px';
    }, 30);
}
